1. Field of the Invention
The present invention relates to a method of measuring and regulating the temperature and quantity of cooling water of a continuous casting mold which flows per unit of time through mold walls composed of copper plates which can be cooled by water, particularly independently of each other.
The present invention also relates to a device for carrying out the method.
2. Description of the Related Art
When continuously casting steel in liquid-cooled plate molds, particularly for producing thin slabs of steel with strand thicknesses of between 150 and 40 mm at comparatively high casting speeds with the use of at least one submerged pouring pipe, initially only a thin strand shell composed of solidified melt and still relatively resilient because of the very high temperature is formed within the mold in the area of the mold outlet opening due to the relatively low thermal conductivity of the steel. Since the strand shell must withstand within the mold and after emerging from the mold the ferrostatic pressure of the melt which is still liquid in the interior, it is necessary that the strand shell has as uniform as possibly a thickness over the entire circumference. The formation of the strand shell depends on a number of interacting factors, such as, casting speed, steel temperature, material, strand geometry, submerged outlet shape, conicality of the mold as well as the type and composition of the slag-forming lubricant which is applied on the meniscus and has the purpose of reducing the unavoidable friction between the strand shell and the mold.
Particularly important in this connection is a uniform distribution of the lubricant in the areas of the mold walls, wherein the lubricant is applied on the meniscus in the form of a so-called casting powder, the lubricant is melted and is moved as a result of oscillating movements of the liquid steel between the steel and the mold walls. A distribution of the lubricant as uniform as possible between the forming strand shell and the mold wall is of particular importance with respect to the heat transfer conditions between the strand shell and the mold wall. By carrying out careful temperature measurements in the areas of the mold walls, conclusions can be made with respect to the distribution of the heat fluxes, particularly over the width of the mold. This is important because, for a safe casting of slabs and especially thin slabs of the above-mentioned type, the knowledge of specific heat transfers at the long sides of the mold and especially in the middle of the slab in the area of the submerged pouring pipe is of particular significance. This makes it possible to prevent or counteract problems in time, wherein these problems may be due, for example, to flow anomalies occurring at the pouring outlet, non-uniform thickness of the lubricating film of casting slag, high membrane effect of the strand shell particularly in the slab middle, turbulences of the meniscus over the width of the slab. Also, it is possible to timely recognize by a temperature measurement the consequences of a non-uniform heat transfer due, for example, to turbulences of the steel in the mold. This is particularly important because the aforementioned anomalies in the casting process, particularly a possible deviation of the strand shell formation from the mold middle, may result in longitudinal cracks in the strand surface and even in ruptures, or so-called stickers. Simultaneously with such problems at the strand shell, corresponding partial thermal loads occur at the copper plates which may lead to a reduction of the service life of the mold.
A number of embodiments and measures for ensuring a safe continuous casting process without the aforementioned disadvantages and difficulties are known in the art. For example, DE 24 15 224 C3 discloses a plate mold for slabs whose walls have cooling chambers which each have defined cooling zones. Connected to the inlet and outlet lines for the cooling water of the long side walls of the mold are measuring units for determining the discharged heat quantity or the cooling capacities. By using these measuring units, an average value of the cooling capacity of the cooling chambers is computed and the average value is supplied to an averaging unit which controls the conicality of the short sides of the mold.
DE 41 17 073 C2 discloses a method of determining the integral and specific heat transport at each individual copper plate of a rectangular or cambered thin slab mold by using calorimetric measurements. A regulation of the short side conicality independently of the individually selected casting parameters is made possible by an on-line comparison of the specific heat fluxes from the copper plate side facing the steel to the water-cooled side specifically of the short sides with those of the long sides.
This method has the disadvantage that with respect to the aforementioned molds no differentiated statements are made with respect to the partial heat fluxes along the mold width. This is also particularly disadvantageous because no determination is made of differentiated specific heat transfers in the areas of the long side walls and especially in the slab middle in the area of the submerged pouring pipe which would produce safe casting of slabs and especially of thin slabs at comparatively high casting speeds. Only when these specific heat transfers are known is it possible to achieve a regulation of the heat fluxes over the entire long side of the mold and thus, over the entire slab width in order to prevent problems especially due to a non-uniform formation of the strand shell.
In order to provide particularly favorable conditions for the casting of thin slabs, a plate mold is known in the art which has water-cooled short side walls which can be clamped between the long side walls, wherein the mold includes devices for adjusting the shape-imparting hollow space to various strand dimensions and for the casting cone, and with an oscillating device. In this mold, the long side walls have at least three cooling segments which are located next to each other and are independent of each other, wherein these cooling segments are distributed symmetrically relative to the middle axis and have in the area of the mold outlet opening special connections for the independent supply of a liquid cooling medium. Temperature sensors are provided in the wall portions of the chambers facing the strand, wherein the temperature sensors are capable of determining at least the temperature differences between the individual chambers or zones.
This division into separate chambers or zones does have the disadvantage that substantially different temperature flows may form on both sides of the separating webs of adjacent chambers or zones, wherein these temperature flows can only be equalized with a relatively long time delay. The known configuration of the cooling segments is not capable in a satisfactory manner to provide a sensitive determination of partial heat fluxes or heat flux differences, for example, over the total width of a mold side wall.